Magnetic and Structural Phases of Monolayer 02 on Graphite

Neutron diffraction studies of O2 thin films physisorbed on the basal plane of graphite show three distinct two-dimensional crystalline phases, all incommensurate with the substrate lattice. The low-temperature monolayer phase has a distorted triangular structure analogous to the closest-packed plane of bulk α-O2. As in α-O2, a magnetic superlattice reflection persisting up to T=10 K indicates a well-developed antiferromagnetic order. Above T=10 K the structure is similar to the closest-packed plane of β-O2.